3GPP for regulating the technical standards of a 3rd mobile communication system has started researches on Long Term Evolution/System Architecture Evolution (LTE/SAE) technology as part of efforts to optimize and improve the performance of 3GPP technologies from the end of the year 2004 in order to handle several forums and new technology related to a 4th mobile communication.
SAE that has been in progress based on 3GPP SA WG2 is research regarding network technology for purposes of determining the structure of a network and supporting mobility between heterogeneous networks, simultaneously with the LTE task of a 3GPP TSG RAN and is one of the recent important standardization issues of 3GPP. In SAE, a task has been in progress for the purpose of an optimized packet-based system with minimized transmission delay through the further improved data transfer capability as a task for developing the 3GPP system into a system that supports various radio access technologies based on an IP.
An SAE higher level reference model defined in 3GPP SA WG2 includes a non-roaming case and roaming cases including various scenarios, and reference can be made to 3GPP standard document TS 23.401 and TS 23.402 for detailed contents of the SAE higher level reference model. A simple reconfiguration of the SAE higher level reference model is shown in a network configuration of FIG. 1.
FIG. 1 shows the structure of an evolved mobile communication network.
One of the greatest characteristics of the network configuration of FIG. 1 is that the network configuration is based on the eNodeB of an evolved UTRAN and a 2 tier model of a gateway of a core network. An eNodeB 20 includes the functions of the NodeB and RNC of an existing UMTS system although not precisely matched, and the gateway can be seen to have the SGSN/GGSN functions of the existing system.
Another important characteristic is that a control plane and a user plane between an access network and a core network are exchanged through different interfaces. In the existing UMTS system, one lu interface is present between the RNC and the SGSN. In contrast, in this network configuration, a Mobility Management Entity (MME) 51 responsible for the processing of control signals is separated from a gateway (GW), and thus an S1-MME and two S1-U interfaces are separately used. The GW include a Serving-GW (hereinafter referred to as an ‘S-GW’) 52 and a Packet Data Network GW (hereinafter referred to as a ‘PDN-GW’ or a ‘P-GW’) 53.
FIG. 2 is a diagram showing a relationship between an (e)NodeB and a Home (e)NodeB.
In the 3rd or 4th mobile communication system, attempts to increase the cell capacity continue to be made in order to support high-capacity service and bidirectional service, such as multimedia content and streaming.
That is, as various high-capacity transmission techniques are demanded in line with the development of communication and the spread of multimedia technology, there is a method of allocating more frequency resources as a method of increasing the radio capacity, but to allocate more frequency resources to a plurality of users using limited frequency resources is limited.
In order to increase the cell capacity, there has been an approach for using a higher frequency band and reducing cell coverage. If a cell having small cell coverage, such as a pico cell, is used, there is an advantage in that more information can be transferred because a band higher than the frequency used in the existing cellular systems can be used. However, there is a disadvantage in that costs are high because more base stations must be installed in the same area.
There has recently been proposed a femto base station, such as a Home (e)NodeB 30, from among approaches for increasing the cell capacity using a small cell as described above.
The Home (e)Node 30 started being researched on the basis of RAN WG3 of a 3GPP Home (e)NodeB and has recently been researched in earnest even in SA WG.
An (e)NodeB 20 shown in FIG. 2 can correspond to a macro base station, and the Home (e)NodeB 30 shown in FIG. 2 can become a femto base station. This specification is described based on the terms of 3GPP, and an (e)NodeB is used when describing a NodeB or an eNodeB. Furthermore, the Home (e)NodeB is used when describing both a Home NodeB and a Home eNodeB.
Interfaces indicated by dotted lines are for transmitting control signals between the (e)NodeB 20 and the Home (e)NodeB 30, and the MME 510. Furthermore, interfaces indicated by solid lines are for transmitting the data of a user plane.
FIG. 3 shows problems according to the prior art.
As shown in FIG. 3, if traffic is overloaded or congested in an interface between an (e)NodeB 20 and an S-GW 52 or traffic is overloaded or congested in an interface between an Home (e)NodeB 30 and the S-GW 52, downlink data toward UE 10 or upload data from the UE 10 is not correctly transmitted, resulting in fail.
Or, if interface between the S-GW 52 and a PDN-GW 53 or an interface between the PDN-GW 53 and an Internet Protocol (IP) service network of a mobile communication service provider is overloaded or congested, downlink data toward the UE 10 or upload data from the UE 10 is not correctly transmitted, resulting in fail.
Furthermore, when UE performs a handover from a current cell from which the UE receives service to another cell, there is a problem in that the service of the UE is dropped if another cell has been overloaded.
In order to solve the problems, mobile communication service providers have changed the S-GW 52 and the PDN-GW 53 to an S-GW and a PDN-GW having a high capacity or have increased new equipment. However, there is a disadvantage in that high costs are necessary. Furthermore, there is a disadvantage in that the S-GW and the PDN-GW having a high capacity or the new equipment is shortly overloaded because the amount of transmitted and received data is increased by geometrical progression.
Meanwhile, there have been proposed various schemes for optimizing the S-GW 52 and the PDN-GW 53 without increasing a mobile communication network as described above. For example, there has been proposed technology in which in a macro access network, specific IP traffic (e.g., Internet service) of UE is transmitted through a selected optimum path, and in a femto access network (e.g., a Home (e)NB), the specific IP traffic is offloaded to a path through the nodes of a public network not a mobile communication network, that is, a wired network, without transmitting and receiving the specific IP traffic to and from a path through a mobile communication network (i.e., selected IP traffic offload).
FIG. 4 shows a concept of Selected IP Traffic Offload (SIPTO).
FIG. 4 illustratively shows a mobile communication system, such as an Evolved Packet System (EPS). The EPS system includes an (e)NodeB 20, an MME 51, an S-GW 52, and a P-GW 53. Furthermore, a Home (e)NodeB 30 is shown.
As shown, in Selected IP Traffic Offload (SIPTO) technology, specific IP traffic (e.g., Internet service) of UE 10 is offloaded to the nodes of a wired network 70 without passing through the nodes within the IP service network 60 of a mobile communication service provider.
For example, when the UE 10 receives grant to access the (e)NodeB 20 or the Home (e)NodeB 30, the UE 10 can generate a session that passes through the wired network 70, such as a public telecommunication network, through the (e)NodeB 20 or the Home (e)NodeB 30 and perform IP network service through the session. Here, service provider policy and subscription information can be taken into consideration.
In order for the session to be generated as described above, a gateway installed in a location close to the (e)NodeB 20 or the Home (e)NodeB 30 may be used as a local gateway responsible for some of the functions of a GGSN in the case of a gateway, that is, a UMTS, or a local gateway responsible for some of the functions of a PDN Gateway (P-GW) in the case of an EPS.
Such a local gateway is called a local GGSN or a local P-GW. The function of the local GGSN or the local P-GW is similar to that of the GGSN or P-GW.
As described above, SIPTO technology has proposed a concept in which the data of UE is offloaded to a wired network, such as a public telecommunication network, through the (e)NodeB 20 or the Home (e)NodeB 30.